Forced Mass on Spring please help

A mass of 2kg is hung on a spring of spring constant 3.92 x 103 Nm-1. The natural frequency for the system is wo = 44.3 s-1. The system is forced to vibrate by an alternating force of amplitude
F = 2 cos (wt) Newtons.
What is the amplitude of vibration when w = 20 s-1